Due to the developments of methods for isolating and purifying natural products, more than 10,000 kinds of antibiotics have been isolated from microorganisms. Further, continued studies on a new identification method and technology, discovery of new isolation resources and application of microbial metabolites to veterinary and agricultural industries have contributed to the development of antibiotics using microorganisms.
Since mutual antagonism between microorganisms was first observed by Tyndall, various antibiotics have been actively developed. For example, actinomycin was isolated from S. antibioticus by Waksman and Woodruff, and streptomycin, from S. griseus by Schatz and Wakman based on the discovery of penicillin by Fleming in 1929. As actinomycin and streptomycin were used for treating pulmonary tuberculosis, Streptomyces has been regarded as an important microorganism for producing antibiotics in the fields of industry and medical sciences. Since metabolites of Streptomyces are very diverse, it can produce various kinds of biologically active substances. Among 10,000 kinds of biologically active substances investigated from microorganisms until now, about two-thirds are found in Streptomyces. Accordingly, the importance of Streptomyces in investigating biologically active substance has been much emphasized. Streptomyces has been regarded as one of the most important microorganisms in biomaterial industry.
Streptomyces is one of the most diverse microbial species and possesses many different biologically metabolic activities even in the same species (Anderson A S, Wellington E M. The taxonomy of Streptomyces and related genera. Int. J. Syst. Evol. Microbiol. 2001, 51(3): 797-814). Accordingly, numerous biologically active substances have been developed from Streptomyces's metabolites, and infinite possibilities of these substances for applying to agricultural and marine industries (breeding, extermination of damages by blight and harmful insects), environmental industry (disposal of wastes), fine chemical industry (technochemical medicines), food industry (raw materials, additives), semiconductor industry (biosensors) and medicine have been suggested.
There have been conducted numerous studies using natural products for the purpose of preventing, alleviating or treating diseases (Emmert E A, Handelsman J. Biocontrol of plant disease: a (Gram−) positive perspective. FEMS Microbiol. Lett. 1999, 1; 171(1): 1-9; Nielsen J. Metabolic engineering: techniques for analysis of targets for genetic manipulations. Biotechnol. Bioeng. 1998, 58(2-3): 125-32; Hutchinson C, Colombo A. Genetic engineering of doxorubicin production in Streptomyces peucetius: J. Ind. Microbiol. Biotechnol. 1999, July; 23(1): 647-652). One of such methods for approaching the purpose is to secure various biological resources. Considering the importance of Streptomyces in biological diversity and industrialization possibility, it is expected to play an important role in practical applicability.
The international agreement to biological diversity relates to preservation of biological diversity, prolonged utilization and fair distribution of profits obtained from the existing genetic resources, and is interested in the preservation of worldwide biological resources. At the point of becoming worse environmental pollution, it has been regarded as an important matter to secure and prevent domestic microbial resources. The United States has approved a patent right for a microorganism since 1980 and the microorganism has become the subject matter of patent since 1987 in the country.
For obtaining a patent right for a microorganism, it is important to analyze exactly the phylogenetical classification of a target microorganism as well as the characteristics of biologically active compounds produced by the microorganism.
The current method for screening a new compound from Streptomyces has been conducted for the purpose of finding a new compound, but it h as often resulted in finding only already patented compounds. Accordingly, it is preferable to carry out the screening of a new compound after a new species or a new strain of Streptomyces is identified, thereby increasing the possibility of discovering new compounds. The classification of Streptomyces has been based on a numerical taxonomy via physiological, morphological or biochemical analyses according to the previously discovered phenotypic features.
However, there are several obstacles in conducting the numerical taxonomy for Streptomyces: exact identification of Streptomyces requires too much time because there are too many subtypes in Streptomyces; Streptomyces has an extremely slow growth rate [cell cycle of E. coli (20 min); cell cycle of Streptomyces (2-3 hrs)]; and its analytical result is not very reliable.
Recently, the numerical taxonomy has been replaced by a molecular taxonomy, which determines a species by analyzing a chronometer molecule showing all bacterial phylogenetic relationship via analyses of nucleotide sequences. Among the chronometer molecules, 16S rDNA molecule has been widely employed for the identification of a microorganism, in particular, Streptomyces. 
The method for identifying a microorganism by sequencing analysis of 16S rDNA has been widely employed in place of the numerical taxonomy using the previous phenotypic features. Further, 16S rDNA has also been employed as a target gene of a kit for detecting a microorganism including pathogenic bacteria by a molecular method (e.g., a gene probing kit for detecting a mycobacterium).
However, there are several drawbacks in the method using 16S rDNA as follows. Although a hypervariable region showing various sequence mutations exists in 16S rDNA, the full-length of 1.5 kb 16S rDNA must be sequenced for the exact identification of a microorganism by comparative sequencing analysis, which is time-consuming and cost-ineffective. This problem raises the problem that too many oligomers should be used to develop a method for identifying a microorganism by a DNA chip in the future. Further, it requires much expense for analyzing the data of 450 kinds or more of species including Streptomyces. Accordingly, while 16S rDNA database of other strains are established at Genbank, that of total Streptomyces species has not been completed except a few species. Besides, it has been reported that 16S rDNA exists in the form of a multi-copy gene in entire chromosomes in some Streptomyces species and the nucleotide sequences of these alleles are different from each other, which becomes a critical defect for the identification method using 16S rDNA (Ueda K, Seki T, Kudo T, Yoshida T, Kataoka M. Two distinct mechanisms cause heterogeneity of 16S rRNA. J. Bacteriol. 1999, January; 181(1): 78-82). Namely, several nucleotide sequences of 16S rDNA exist in one strain, and this raises a technical problem in sequencing analysis. Because it is not possible to directly analyze the nucleotide sequence of a PCR product after PCR amplification of the target gene of Streptomyces, the amplified product must be cloned into a vector and several clones thus obtained are subjected to sequencing analysis.
Due to these problems, it is necessary to select a new chronometer molecule besides 16S rDNA for the identification of Streptomyces. 
Potato scab is a pathogenic disease caused by three different Streptomyces species of S. scabiei, S. acidiscabies and S. turgidiscabies, with rare exceptions of a few Streptomyces species. Of them, S. scabiei is the major pathogenic microorganism which is composed of many genetical side groups.
Since Streptomyces is the most diverse species with a relatively slow growth rate as compared to other microorganisms, it is very difficult to classify Streptomyces species by a biochemical or physiological method (Skerman, V. B. D., McGowan, V., Sneath, P. H. A. (ed): Approved Lists of Bacterial Names. Int. J. Syst. Bacteriol. 1980, 30: 225-420). Therefore, several methods, e.g., a fatty acid analyzing method, DNA-DNA hybridization method and 16S rRNA gene analyzing method, have been developed for identifying a potato scab pathogenic microorganism. Of these methods, the method for analyzing 16S rRNA has an advantage in defining a phylogenetic relationship between microorganisms or identifying an unknown strain and has been effectively used for identifying pathogenic bacteria. However, it is very difficult to exactly classify bacterial strains showing close phylogenetic relationship among them because the nucleotide sequence of 16S rRNA is highly conserved in these strains. Accordingly, there is a need of establishing a method for identifying a potato scab pathogenic microorganism using a new substitute gene for 16S rRNA. To compensate the defect of 16S rRNA analyzing method, there was developed a method for identifying an unknown strain using 16S-23S ITS region as a target gene, a region known to be more hypervariable than 16S rDNA. However, this method is not suitable for the classification and identification of a potato scab pathogenic microorganism because 16S-23S ITS target gene has a few different nucleotide sequences in each individual. Therefore, it has been a long-awaited need to develop a method for identifying a potato scab pathogenic microorganism using a new chronometer molecule as a target gene.
The present inventors have therefore endeavored to find a method that meets the above need, and developed a method for identifying Streptomyces species using groEL2 gene which comprises the steps of preparing a specific primer for groEL2 gene conserved in all Streptomyces species; amplifying groEL2 gene using the primer; sequencing the nucleotide sequence of amplified product to build a database; and identifying unknown Streptomyces species using the database.